impexptime shows the running time of Phase II - the symmetric Tucker decomposition.
The vertical axes plot the relative gradient as a measure of convergence precision, as used in [1]}, [2]}, [3]}:
\(\texttt {relative~gradient} := \frac{\Vert \text{grad}~F(\mathbf {Q})\Vert }{F(\mathbf {Q})}.\) 
